The Georgia Bureau of Investigation is investigating a shooting involving an off-duty Atlanta police officer at an apartment complex on Christmas Eve.

The shooting happened around 11:45 p.m. at The Commons apartments on the 3000 block of Middleton Road, officials said.

According to an Atlanta Police Department spokesperson, the officer was working an extra job at the complex when he heard gunfire and was flagged down by two people.

The two people told the officer that a man armed with a gun was chasing a woman in the complex and had shot her.

Authorities say the officer arrived at the scene and found 31-year-old Joshua Knox holding a gun. After Knox did not comply with the officer's demands to drop the weapon, the officer fired at least one shot, hitting him, the GBI said.

Medics rushed Knox to Grady Memorial Hospital for treatment. He is expected to survive his injuries.

The GBI will do its own investigation into the shooting, as is standard for any shooting involving police officers in the state.